The present invention relates to an electronic circuit for multiplying together two voltage signals.
A particular application of the invention lies in AC electrical energy meters for measuring energy consumption, e.g. of subscribers to mains. Under such circumstances, the voltage signals to be multiplied together represent the voltage and the current delivered to a load as constituted by the electrical installations mounted downstream from the meter.
Voltage multiplier circuits are known that are completely analog, using amplifiers having logarithmic and exponential responses. Such amplifiers require temperature and time compensations that give rise to non-linearities and to offsets that increase with decreasing magnitude of the signals to be multiplied together. Such compensations are difficult to implement accurately over the entire operating range of the circuit.
Potentiometer multiplier circuits are also known in which one of the voltages to be multiplied is converted into a digital value that is used for controlling the position of a potentiometer wiper. The potentiometer receives the other voltage to be multiplied, and its output delivers a signal proportional to the product. When high resolution is required, the potentiometer must comprise a large number of resistors connected in series. In order to ensure that the response of the circuit is linear, the various resistors must have characteristics that are as uniform as possible. The greater the number of resistors in the potentiometer, the more difficult this condition is to achieve. Known potentiometer circuits are therefore difficult to optimize simultaneously in terms of resolution and of accuracy.